The present invention relates to a sorting system for flat mail items, said system comprising at least three storage modules connected in a parallel arrangement, wherein each of the at least three storage modules comprises a storage area and an infeed function which transfers mail items from a stream of mail items into the storage area, and an extraction function which extracts mail items from the storage area for the purpose of generating an optimized stream of mail items.
With present-day mail sorting systems, very large quantities of mail items sometimes have to be sorted and distributed in what are referred to as mail centers and/or major post offices. Thus, for example, the average daily volume of mail handled in Germany amounts to approximately 80 million mailings, which are required to reach their addressees already on the very next day or at the latest on the next day but one after posting. Mail items of this kind are generally referred to as “letters”. Said mail items are characterized in that their length and width are generally large compared with their height. However, there are sometimes significant differences between the postal administration authorities of the different national states with regard to the definitive dimensions used for assigning mail items to this “letters” group. As well as these size variations it can also easily be seen that the properties of the mail items, even when they are all “letters” may differ considerably from one to another in certain cases.
It is therefore easy to imagine that mail automation processes today have to be operated with a high degree of efficiency and, as a result of cost pressure, also with a comparatively small number of operators. To achieve sufficiently high throughput rates in the sorting machines, the mail items are conveyed through the sorting machine at speeds of up to 4 m/s and in places even more, and are sorted to their destination by means of appropriately switched diverters and a sophisticated, usually multi-stage delivery route sequencing sorting method.
To ensure correct delivery of the mail items it is therefore essential that the address of the mail item can be properly registered once by automated means at least at the beginning of the sorting process. Frequently, however, the address is not machine-readable but must be added by entering the address (or at least the part thereof which is significant for the current sorting process) manually. This fact makes it necessary for the non-machine-readable mail items to be filtered out of the sorting process and buffered while the address is manually assigned. Following manual address assignment, they must then be extracted from the buffer once more and can be fed back into the sorting process.
This buffering is currently achieved by means of what are referred to as storage conveyors on which the incoming individual mail items are transported at a minimum spacing until the time required for interpreting the address and for registering at least certain significant parts of the address has elapsed. Typically, an image which can be read by operators (people) is generated of a non-machine-readable address, the operators then entering the recognized address into the control system, as a result of which the manually entered address is assigned to the mail item and at the next opportunity in the sorting process is printed onto the mail item, usually in the form of a barcode.
A critical factor in dimensioning the length of said storage conveyor is therefore the processing time for recognizing the address and entering and assigning the registered address data to the mail item previously not (correctly) recognized with regard to its address. At the given speeds (as a function of the envisioned throughput) there therefore result storage conveyors which very quickly reach lengths of 50 m or even more. Since the gap displacements between the mail items are approximately proportional to the transport length on the storage conveyor, a corresponding loss in throughput is therefore also associated with a long storage conveyor, because the gap displacements have to be made available in addition to a required minimum gap between two adjacent mail items. Furthermore the storage conveyor itself is attended by a number of disadvantages, because, of course, a correspondingly long storage conveyor also takes up a relatively large amount of space and, of course, also has to be installed, operated and maintained. In order to be able nonetheless to use the generally limited amount of space available in a sorting center as efficiently as possible, the storage conveyor usually runs with a multiple fold, although this also leads to a folding of the mail items and consequently unfortunately also sometimes to considerable damage to the mail items.
As a result of these restrictions the storage conveyor is therefore always set to a certain minimum. This means that the mail items can be evaluated only to a limited depth in terms of information, which on the one hand results in the absence of information depth as regards the address resolution, the completeness of which would, however, be necessary for the delivery route sequencing, leading to additional processing steps. On the other hand this leads to the mail items only being evaluated with a great frequency, which means that the mail items that have not been evaluated have to be processed automatically once again or just have to be processed manually.